Trachyte () is an

extrusive Extrusive rock refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff. In contr ...

igneous rock Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...

composed mostly of

alkali feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocla ...

. It is usually light-colored and

aphanitic Aphanites (adj. ''aphanitic''; ) are igneous rocks that are so fine-grained that their component mineral crystals are not visible to the naked eye (in contrast to phanerites, in which the crystals are visible to the unaided eye). This geo ...

(fine-grained), with minor amounts of

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

minerals, and is formed by the rapid cooling of lava (or shallow intrusions) enriched with silica and

alkali metal The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...

s. It is the volcanic equivalent of

syenite Syenite is a coarse-grained intrusive igneous rock with a general composition similar to that of granite, but deficient in quartz, which, if present at all, occurs in relatively small concentrations (< 5%). It is considered a Trachyte is common wherever alkali magma is erupted, including in late stages of ocean island volcanismMacDonald 1983, pp. 51–52 and in continental

rift valley A rift valley is a linear shaped lowland between several highlands or mountain ranges produced by the action of a geologic rift. Rifts are formed as a result of the pulling apart of the lithosphere due to extensional tectonics. The linear ...

s, above

mantle plume A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic ho ...

s,Philpotts and Ague 2009, pp. 390–394 and in areas of

back-arc The back-arc region is the area behind a volcanic arc. In island arc, island volcanic arcs, it consists of back-arc basins of oceanic crust with abyssal zone, abyssal depths, which may be separated by remnant arcs, similar to island arcs. In conti ...

extension. Trachyte has also been found in

Gale crater Gale is a crater, and probable dry lake, at in the northwestern part of the Aeolis quadrangle on Mars. It is in diameter and estimated to be about 3.5–3.8 billion years old. The crater was named after Walter Frederick Gale, an amateur a ...

on Mars. Trachyte has been used as decorative building stone and was extensively used as

dimension stone Dimension stone is natural stone or Rock (geology), rock that has been selected and finished (e.g., trimmed, cut, drilled or ground) to specific sizes or shapes. Color, Texture (geology), texture and pattern, and surface finish of the stone are ...

in the

Roman Empire The Roman Empire ruled the Mediterranean and much of Europe, Western Asia and North Africa. The Roman people, Romans conquered most of this during the Roman Republic, Republic, and it was ruled by emperors following Octavian's assumption of ...

and the

Republic of Venice The Republic of Venice, officially the Most Serene Republic of Venice and traditionally known as La Serenissima, was a sovereign state and Maritime republics, maritime republic with its capital in Venice. Founded, according to tradition, in 697 ...

Chemical composition

Trachyte has a silica content of 60 to 65% and an alkali oxide content of over 7%. This gives it less SiO₂ than

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...

and more (Na₂O plus K₂O) than

dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. ...

. These chemical differences are consistent with the position of trachyte in the

TAS classification TAS stands for Total Alkali Silica. The TAS classification can be used to assign names to many common types of volcanic rocks based upon the relationships between the combined alkali and silica contents. These chemical parameters are useful because ...

, and they account for the feldspar-rich mineralogy of the rock type. Trachydacite occupies the same field in the TAS diagram as trachyte, but is distinguished from trachyte by a

normative Normativity is the phenomenon in human societies of designating some actions or outcomes as good, desirable, or permissible, and others as bad, undesirable, or impermissible. A Norm (philosophy), norm in this sense means a standard for evaluatin ...

quartz content over 20%. Trachydacite is not a recognized rock type in the QAPF classification, where rocks rich in alkali feldspar and with quartz over 20% would be classified as rhyolites.

Mineralogy

The mineral assemblage of trachytes consists of essential alkali feldspar. Relatively minor

plagioclase Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...

and

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

or a

feldspathoid The feldspathoids are a group of tectosilicate minerals which resemble feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, pota ...

such as

nepheline Nepheline, also called nephelite (), is a rock-forming mineral in the feldspathoid groupa silica-undersaturated aluminosilicate, Na3 K Al4 Si4 O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatit ...

may also be present.Philpotts and Ague 2009, pp. 369–370 This is reflected in the position of the trachyte fields in the

QAPF diagram A QAPF diagram is a doubled-triangle plot diagram used to classify igneous rocks based on their mineralogy. The acronym QAPF stands for "quartz, alkali feldspar, plagioclase, feldspathoid (foid)", which are the four mineral groups used for clas ...

Biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron- endmember annite, and the magnesium-endmember phlogopite; more al ...

clinopyroxene The pyroxenes (commonly abbreviated Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents ions of calcium (Ca), sodium (Na), iron (Fe ...

and

olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...

are common accessory minerals. The plagioclase is typically sodium-rich

oligoclase Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. In chemical composition and in its crystallographic and physical characters it is intermediate between albite ( Na Al Si3 O8) and anorthite ( CaAl2Si2O8). The albite:ano ...

. The alkali feldspar is typically also sodium-rich

sanidine Sanidine is the high temperature form of potassium feldspar with a general formula K(AlSi3O8). Sanidine is found most typically in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the monoclinic crystal sys ...

(

anorthoclase The mineral anorthoclase ((Na,K)AlSi3O8) is a crystalline solid solution in the alkali feldspar series, in which the proportion of the sodium-aluminium silicate member exceeds the potassium-aluminium silicate member. It typically consists of bet ...

) and is often cryptoperthitic, with alternating microscopic bands of sodium feldspar (

albite Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula . It is a tectosilicat ...

) and potassium feldspar (sanidine). Trachytes are typically fine-grained and light-colored, but can be black if they consist mostly of glass.MacDonald 1983, p. 128 They are often porphyritic, with large well-shaped crystals of sanidine in a

groundmass The matrix or groundmass of a rock is the finer-grained mass of material in which larger grains, crystals, or clasts are embedded. The matrix of an igneous rock consists of finer-grained, often microscopic, crystals in which larger crystals, ...

containing much smaller imperfect sanidine laths.

Rhomb porphyry Porphyry ( ) is any of various granites or igneous rocks with coarse-grained crystals such as feldspar or quartz dispersed in a fine-grained silicate-rich, generally aphanitic matrix or groundmass. In its non-geologic, traditional use, the ...

is an example with usually large

porphyritic Porphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts. Both extrusive and intrusive rocks can be porphyritic, meaning ...

rhomb In plane Euclidean geometry, a rhombus (: rhombi or rhombuses) is a quadrilateral whose four sides all have the same length. Another name is equilateral quadrilateral, since equilateral means that all of its sides are equal in length. The rhom ...

shaped

phenocrysts 300px, Swiss side of the Mont Blanc massif, has large white phenocrysts of plagioclase (that have trapezoid shapes when cut through). 1 euro coin (diameter 2.3 cm) for scale. A phenocryst is an early forming, relatively large and usually conspic ...

embedded in a very fine-grained

matrix Matrix (: matrices or matrixes) or MATRIX may refer to: Science and mathematics * Matrix (mathematics), a rectangular array of numbers, symbols or expressions * Matrix (logic), part of a formula in prenex normal form * Matrix (biology), the m ...

. Some of the best known trachytes, such as the trachyte of Drachenfels on the Rhine, show striking porphyritic character, having large sanidine crystals of tabular form an inch or two in length scattered through their fine-grained groundmass. In many trachytes, however, the phenocrysts are few and small, and the groundmass comparatively coarse. The ferromagnesian minerals rarely occur in large crystals, and are usually not conspicuous in hand-sized specimens of these rocks. Two types of groundmass are generally recognized: the trachytic, composed mainly of long, narrow, subparallel rods of sanidine, and the orthophyric, consisting of small squarish or rectangular prisms of the same mineral. Sometimes granular augite or spongy riebeckite occurs in the groundmass, but as a rule this part of the rock is highly feldspathic. Trachytes very often have minute irregular

vesicles Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane * Synaptic vesicle In a neuron, synaptic vesicles (or neurotransmitter vesicles) s ...

which make the broken surfaces of specimens of these rocks rough and irregular, and it is from this distinctive texture that they received their name. It was first given to rocks of this class from

Auvergne Auvergne (; ; or ) is a cultural region in central France. As of 2016 Auvergne is no longer an administrative division of France. It is generally regarded as conterminous with the land area of the historical Province of Auvergne, which was dis ...

, and was long used in a much wider sense than that defined above, so that it included quartz-trachytes (now known as liparites and

s) and

-trachytes, which are now classified as

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...

s. Quartz is rare in trachyte, but

tridymite Tridymite is a high-temperature polymorphism (materials science), polymorph of silica and usually occurs as minute tabular white or colorless pseudo-hexagonal crystals, or scales, in cavities in felsic volcanic rocks. Its chemical formula is sili ...

(which likewise consists of

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...

) is not uncommon. It is rarely in crystals large enough to be visible without the aid of the

microscope A microscope () is a laboratory equipment, laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic ...

, but in

thin section In optical mineralogy and petrography, a thin section (or petrographic thin section) is a thin slice of a rock or mineral sample, prepared in a laboratory, for use with a polarizing petrographic microscope, electron microscope and electron ...

s it may appear as small hexagonal plates, which overlap and form dense aggregates, like a mosaic or like the tiles on a roof. They often cover the surfaces of the larger feldspars or line the vesicles of the rock, where they may be mingled with amorphous

opal Opal is a hydrated amorphous form of silicon dioxide, silica (SiO2·''n''H2O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Due to the amorphous (chemical) physical structure, it is classified as a ...

or fibrous

chalcedony Chalcedony ( or ) is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic ...

. In the older trachytes, secondary quartz from the recrystallization of tridymite is not rare. Of the

minerals present,

augite Augite, also known as Augurite, is a common rock-forming pyroxene mineral with formula . The crystals are monoclinic and prismatic. Augite has two prominent cleavages, meeting at angles near 90 degrees. Characteristics Augite is a solid soluti ...

is the most common. It is usually of pale green color, and its small crystals are often very perfect in form. Brown

hornblende Hornblende is a complex silicate minerals#Inosilicates, inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common ...

and biotite occur also, and are usually surrounded by black corrosion borders composed of

magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula . It is one of the iron oxide, oxides of iron, and is ferrimagnetism, ferrimagnetic; it is attracted to a magnet and can be magnetization, magnetized to become a ...

and

pyroxene The pyroxenes (commonly abbreviated Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents ions of calcium (Ca), sodium (Na), iron ( ...

; sometimes the replacement is complete and no hornblende or biotite is left, though the outlines of the cluster of magnetite and augite may clearly indicate from which of these minerals it was derived. Olivine is unusual, though found in some trachytes, for example those of the Arso in

Ischia Ischia ( , , ) is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about from the city of Naples. It is the largest of the Phlegrean Islands. Although inhabited since the Bronze Age, as a Ancient G ...

. Basic varieties of plagioclase, such as

labradorite Labradorite (( Ca, Na)( Al, Si)4 O8) is a calcium-enriched feldspar mineral first identified in Labrador, Canada, which can display an iridescent effect ( schiller). Labradorite is an intermediate to calcic member of the plagioclase series. It ...

, are known also as phenocrysts in some Italian trachytes. Dark brown varieties of augite and rhombic pyroxene (

hypersthene Hypersthene is a common rock-forming inosilicate mineral belonging to the group of orthorhombic pyroxenes. Its chemical formula is . It is found in igneous and some metamorphic rocks as well as in stony and iron meteorites. Many references have f ...

bronzite Bronzite is a member of the pyroxene group of minerals, belonging with enstatite and hypersthene to the orthorhombic series of the group. Rather than a distinct species, it is really a ferriferous variety of enstatite, which owing to partial alt ...

) have been observed but are not common.

Apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of Hydroxide, OH−, Fluoride, F− and Chloride, Cl− ion, respectively, in the crystal. The formula of the admixture of ...

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of th ...

and magnetite are practically always present as accessory minerals. Occasionally minerals of the

group, such as

sodalite Sodalite ( ) is a tectosilicate mineral with the formula , with royal blue varieties widely used as an ornamental gemstone. Although massive sodalite samples are opaque, crystals are usually transparent to translucent. Sodalite is a member of th ...

and

leucite Leucite (from the Greek word ''leukos'' meaning white) is a rock-forming mineral of the feldspathoid group, silica-undersaturated and composed of potassium and aluminium tectosilicate KAlSi2O6. Crystals have the form of cubic icositetrahedra b ...

, are present in trachytes, and rocks of this kind are known as foid-bearing trachytes.Blatt and Tracy 1996, p.74 The sodium-bearing

amphibole Amphibole ( ) is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is ...

s and pyroxenes so characteristic of the phonolites may also be found in some trachytes; thus

aegirine Aegirine is a member of the clinopyroxene group of inosilicate minerals. It is the sodium endmember of the aegirine– augite series. It has the chemical formula NaFeSi2O6, in which the iron is present as the ion Fe3+. In the aegirine–augite se ...

or aegirine augite forms outgrowths on

diopside Diopside is a monoclinic pyroxene mineral with composition . It forms complete solid solution series with hedenbergite () and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull ...

crystals, and

riebeckite Riebeckite is a sodium-rich member of the amphibole group of silicate minerals, chemical formula Na2(Fe2+3Fe3+2)Si8O22(OH)2. It forms a solid solution series with magnesioriebeckite. It crystallizes in the monoclinic system, usually as long ...

may be present in spongy growths among the feldspars of the groundmass (as in the trachyte of Berkum on the

Rhine The Rhine ( ) is one of the List of rivers of Europe, major rivers in Europe. The river begins in the Swiss canton of Graubünden in the southeastern Swiss Alps. It forms part of the Swiss-Liechtenstein border, then part of the Austria–Swit ...

). Glassy forms of trachyte (

obsidian Obsidian ( ) is a naturally occurring volcanic glass formed when lava extrusive rock, extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock. Produced from felsic lava, obsidian is rich in the lighter element ...

) occur, as in

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

, and

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of extremely vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicula ...

ous varieties are known (in Tenerife and elsewhere), but these rocks as contrasted with the rhyolites have a remarkably strong tendency to crystallize, and are rarely to any considerable extent vitreous.

Geographic distribution

Trachyte is the usual silica-rich end member of the

alkaline magma series The alkaline magma series is a chemically distinct range of magma compositions that describes the evolution of an Alkaline volcanic rock, alkaline mafic magma into a more evolved, silica-rich end member. Geochemical characterization Rocks in t ...

, in which alkaline basaltic magma experiences

fractional crystallization Fractional crystallization may refer to: * Fractional crystallization (chemistry), a process to separate different solutes from a solution * Fractional crystallization (geology) Fractional crystallization, or crystal fractionation, is one of the ...

while still underground. This process removes calcium, magnesium, and iron from the magma to give it a composition close to that of alkali feldspar. As a result, trachyte is common wherever alkali magma is erupted, including late eruptions of ocean islands and in continental

s and

s. Only rarely does magmatic differentiation proceed beyond trachyte to

phonolite Phonolite is an uncommon shallow intrusive or extrusive rock, of intermediate chemical composition between felsic and mafic, with texture ranging from aphanitic (fine-grained) to porphyritic (mixed fine- and coarse-grained). Phonolite is a var ...

or even more evolved alkaline magmas. Trachyte also occurs in areas of

extension, such as the northern

Aegean Sea The Aegean Sea is an elongated embayment of the Mediterranean Sea between Europe and Asia. It is located between the Balkans and Anatolia, and covers an area of some . In the north, the Aegean is connected to the Marmara Sea, which in turn con ...

and the Aeolian arc of Italy. The Aeolian back-arc includes the

Campi Flegrei The Phlegraean Fields (, ; ) is a large volcanic caldera west of Naples, Italy. The Neapolitan Yellow Tuff eruption (about 12ka BP) produced just 50 cubic kilometers. It is, however, one of relatively few volcanoes large enough to form a cal ...

volcanic field, where trachytes have been erupted. Trachytes are well represented among the

Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...

volcanic rocks of Europe. In

Britain Britain most often refers to: * Great Britain, a large island comprising the countries of England, Scotland and Wales * The United Kingdom of Great Britain and Northern Ireland, a sovereign state in Europe comprising Great Britain and the north-eas ...

they occur in

Skye The Isle of Skye, or simply Skye, is the largest and northernmost of the major islands in the Inner Hebrides of Scotland. The island's peninsulas radiate from a mountainous hub dominated by the Cuillin, the rocky slopes of which provide some o ...

lava flow Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

s and as dikes or intrusions, but they are much more common on the continent of Europe, as in the Rhine district and the

Eifel The Eifel (; , ) is a low mountain range in western Germany, eastern Belgium and northern Luxembourg. It occupies parts of southwestern North Rhine-Westphalia, northwestern Rhineland-Palatinate and the southern area of the German-speaking Com ...

, also in Auvergne,

Bohemia Bohemia ( ; ; ) is the westernmost and largest historical region of the Czech Republic. In a narrow, geographic sense, it roughly encompasses the territories of present-day Czechia that fall within the Elbe River's drainage basin, but historic ...

and the

Euganean Hills The Euganean Hills ( ) are a group of hills of volcanic origin that rise to heights of 300 to 600 m from the Padovan-Venetian plain a few km south of Padua. The ''Colli Euganei'' form the first Regional park established in the Veneto (1989), enc ...

. In the neighborhood of Rome,

Naples Naples ( ; ; ) is the Regions of Italy, regional capital of Campania and the third-largest city of Italy, after Rome and Milan, with a population of 908,082 within the city's administrative limits as of 2025, while its Metropolitan City of N ...

and the island of

trachytic

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

s and

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock co ...

s are of common occurrence. Trachytes are also found on the island of

Pantelleria Pantelleria (; ), known in ancient times as Cossyra or Cossura, is an Italian island and comune in the Strait of Sicily in the Mediterranean Sea, southwest of Sicily and east of the Tunisian coast. On clear days Tunisia is visible from the ...

. In the United States, trachytes crop out extensively in the

Davis Mountains The Davis Mountains, originally known as Limpia Mountains, are a range of mountains in West Texas, United States, located near Fort Davis, Texas, Fort Davis, after which they are named. The fort was named for then-United States Secretary of War ...

Chisos Mountains The Chisos Mountains, also known as the Chisos, are a mountain range located in the Big Bend, Texas, Big Bend area of the Trans-Pecos region of Texas, United States. The mountain system covers 40 square miles (104 square km) and is contained enti ...

, and

Big Bend Ranch State Park Big Bend Ranch State Park is a state park located on the Rio Grande in Brewster and Presidio counties, Texas. It is the largest state park in Texas. The closest major town is Presidio, Texas. The state park's head office is located in Lajitas, ...

in the

Big Bend (Texas) The Big Bend is part of the Trans-Pecos region in southwestern Texas, United States along the border with Mexico, north of the prominent bend in the Rio Grande for which the region is named. Here the Rio Grande passes between the Chisos Moun ...

region, as well as southern

Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...

and

South Dakota South Dakota (; Sioux language, Sioux: , ) is a U.S. state, state in the West North Central states, North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Dakota people, Dakota Sioux ...

(

Black Hills The Black Hills is an isolated mountain range rising from the Great Plains of North America in western South Dakota and extending into Wyoming, United States. Black Elk Peak, which rises to , is the range's highest summit. The name of the range ...

). There is one known voluminous flow from Puʻu Waʻawaʻa on the north flank of

Hualālai Hualālai (pronounced in Hawaiian) is an active volcano on the island of Hawaii in the Hawaiian Islands. It is the westernmost, third-youngest and the third-most active of the five volcanoes that form the island of Hawaii, following Kīlauea ...

in Hawaiʻi. Here the trachyte is glassy and black in color.MacDonald 1983, p. 128 In Iceland, the

Azores The Azores ( , , ; , ), officially the Autonomous Region of the Azores (), is one of the two autonomous regions of Portugal (along with Madeira). It is an archipelago composed of nine volcanic islands in the Macaronesia region of the North Atl ...

Tenerife Tenerife ( ; ; formerly spelled ''Teneriffe'') is the largest and most populous island of the Canary Islands, an Autonomous communities of Spain, autonomous community of Spain. With a land area of and a population of 965,575 inhabitants as of A ...

and

Ascension Ascension or ascending may refer to: Religion * "Ascension", the belief in some religions that some individuals have ascended into Heaven without dying first. The Catholic concept of the Assumption of Mary leaves open the question of her deat ...

there are recent trachytic lavas, and rocks of this kind occur also in

New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...

( Cambewarra Range), Queensland ( Main Range), East Africa,

Madagascar Madagascar, officially the Republic of Madagascar, is an island country that includes the island of Madagascar and numerous smaller peripheral islands. Lying off the southeastern coast of Africa, it is the world's List of islands by area, f ...

Yemen Yemen, officially the Republic of Yemen, is a country in West Asia. Located in South Arabia, southern Arabia, it borders Saudi Arabia to Saudi Arabia–Yemen border, the north, Oman to Oman–Yemen border, the northeast, the south-eastern part ...

and in many other districts. Among the older volcanic rocks trachytes also are not scarce, though they have often been described under the names orthophyre and orthoclase-porphyry, while trachyte was reserved for

Tertiary Tertiary (from Latin, meaning 'third' or 'of the third degree/order..') may refer to: * Tertiary period, an obsolete geologic period spanning from 66 to 2.6 million years ago * Tertiary (chemistry), a term describing bonding patterns in organic ch ...

and recent rocks of similar composition. In England there are

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

trachytes in the Exeter district, and

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

trachytes are found in many parts of the central valley of Scotland. The latter differ in no essential respect from their modern representatives in Italy and the

valley, but their augite and biotite are often replaced by

chlorite The chlorite ion, or chlorine dioxide anion, is the halite (oxyanion), halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as s ...

and other secondary products. Permian trachytes occur also in

Thuringia Thuringia (; officially the Free State of Thuringia, ) is one of Germany, Germany's 16 States of Germany, states. With 2.1 million people, it is 12th-largest by population, and with 16,171 square kilometers, it is 11th-largest in area. Er ...

and the

Saar Saar or SAAR has several meanings: People Given name * Sarr Boubacar (born 1951), Senegalese professional football player * Saar Ganor, Israeli archaeologist * Saar Klein (born 1967), American film editor Surname * Ain Saar (born 1968), E ...

district in Germany. Alkaline rocks such as trachyte are rare in the

Archean The Archean ( , also spelled Archaean or Archæan), in older sources sometimes called the Archaeozoic, is the second of the four geologic eons of Earth's history of Earth, history, preceded by the Hadean Eon and followed by the Proterozoic and t ...

, but become common in the

Proterozoic The Proterozoic ( ) is the third of the four geologic eons of Earth's history, spanning the time interval from 2500 to 538.8 Mya, and is the longest eon of Earth's geologic time scale. It is preceded by the Archean and followed by the Phanerozo ...

. Alkaline rocks with an age close to 570 million years are common around the perimeters of many

continental shield A shield is a large area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas. These rocks are older than 570 million years and sometimes date back to around 2 to 3.5 billion years. T ...

s and are evidence of worldwide rifting at that time.Philpotts and Ague 2009, pp. 390–391 Closely allied to trachyte is the rock type called

keratophyre Keratophyre is a volcanic rock of intermediate composition. Although similar to trachyte, keratophyre's plagioclase component is richer in sodium than the plagioclase found in trachyte. Keratophyre forms lava flows and subvolcanic intrusions ( dyk ...

, which is the sodium-rich-plagioclase equivalent of trachyte.

Notes

External links

Porphyritic trachyte hand specimen

{{Authority control Volcanology Volcanic rocks Felsic rocks

Chemical composition

Mineralogy

Geographic distribution

See also

Notes

External links